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LRU cache implementation.

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Vladimir Byko-Ianko 2018-03-29 14:40:52 +03:00 • committed by mpimenov
parent d79084767f
commit c37441bf50
3 changed files with 169 additions and 0 deletions
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1
base/CMakeLists.txt
View file

@ -42,6 +42,7 @@ set(
logging.cpp
logging.hpp
lower_case.cpp
lru_cache.hpp
macros.hpp
math.hpp
matrix.hpp

164
base/lru_cache.hpp Normal file
View file

@ -0,0 +1,164 @@
#pragma once
#include "base/assert.hpp"
#include <cstddef>
#include <functional>
#include <map>
#include <unordered_map>
/// \brief Implementation of cache with least recently used replacement policy.
template <typename Key, typename Value>
class LruCache
{
template <typename K, typename V> friend class LruCacheTest;
template <typename K, typename V> friend class LruCacheKeyAgeTest;
public:
using Loader = std::function<void(Key const & key, Value & value)>;
/// \param maxCacheSize Maximum size of the cache in number of items. It should be one or greater.
/// \param loader Function which is called if it's necessary to load a new item for the cache.
/// For the same |key| should be loaded the same |value|.
LruCache(size_t maxCacheSize, Loader const & loader)
: m_maxCacheSize(maxCacheSize), m_loader(loader)
{
CHECK_GREATER(maxCacheSize, 0, ());
}
/// \brief Loads value, if it's necessary, by |key| with |m_loader|, puts it to |m_cache| and
/// returns the reference to the value to |m_cache|.
Value const & GetValue(Key const & key)
{
auto const it = m_cache.find(key);
if (it != m_cache.cend())
{
m_keyAge.UpdateAge(key);
return it->second;
}
if (m_cache.size() >= m_maxCacheSize)
{
m_cache.erase(m_keyAge.GetLruKey());
m_keyAge.RemoveLru();
}
m_keyAge.InsertKey(key);
Value & value = m_cache[key];
m_loader(key, value);
return value;
}
/// \brief Checks for coherence class params.
/// \note It's a time consumption method and should be called for tests only.
bool IsValid() const
{
if (!m_keyAge.IsValidForTesting())
return false;
for (auto const & kv : m_cache)
{
if (!m_keyAge.IsKeyValidForTesting(kv.first))
return false;
}
return true;
}
private:
/// \brief This class support cross mapping from age to key and for key to age.
/// It lets effectively get least recently used key (key with minimum value of age)
/// and find key age by its value to update the key age.
/// \note Size of |m_ageToKey| and |m_ageToKey| should be the sameß.
/// All keys of |m_ageToKey| should be values of |m_ageToKey| and on the contrary
/// all keys of |m_ageToKey| should be values of |m_ageToKey|.
/// \note Ages should be unique for all keys.
class KeyAge
{
template <typename K, typename V> friend class LruCacheKeyAgeTest;
public:
/// \brief Increments |m_age| and insert key to |m_ageToKey| and |m_keyToAge|.
/// \note This method should be used only if there's no |key| in |m_ageToKey| and |m_keyToAge|.
void InsertKey(Key const & key)
{
++m_age;
m_ageToKey[m_age] = key;
m_keyToAge[key] = m_age;
}
/// \brief Increments |m_age| and updates key age in |m_ageToKey| and |m_keyToAge|.
/// \note This method should be used only if there's |key| in |m_ageToKey| and |m_keyToAge|.
void UpdateAge(Key const & key)
{
++m_age;
auto keyToAgeIt = m_keyToAge.find(key);
CHECK(keyToAgeIt != m_keyToAge.end(), ());
// Removing former age.
size_t const removed = m_ageToKey.erase(keyToAgeIt->second);
CHECK_EQUAL(removed, 1, ());
// Putting new age.
m_ageToKey[m_age] = key;
m_keyToAge[key] = m_age;
}
/// \returns Least recently used key without updating the age.
/// \note |m_ageToKey| and |m_keyToAge| shouldn't be empty.
Key const & GetLruKey() const
{
CHECK(!m_ageToKey.empty(), ());
// The smaller age the older item.
return m_ageToKey.cbegin()->second;
}
void RemoveLru()
{
Key const & lru = GetLruKey();
size_t const removed = m_keyToAge.erase(lru);
CHECK_EQUAL(removed, 1, ());
m_ageToKey.erase(m_ageToKey.begin());
}
/// \brief Checks for coherence class params.
/// \note It's a time consumption method and should be called for tests only.
bool IsValidForTesting() const
{
for (auto const & kv : m_ageToKey)
{
if (kv.first > m_age)
return false;
if (m_keyToAge.find(kv.second) == m_keyToAge.cend())
return false;
}
for (auto const & kv : m_keyToAge)
{
if (kv.second > m_age)
return false;
if (m_ageToKey.find(kv.second) == m_ageToKey.cend())
return false;
}
return true;
}
/// \returns true if |key| and its age are contained in |m_keyToAge| and |m_keyToAge|.
/// \note It's a time consumption method and should be called for tests only.
bool IsKeyValidForTesting(Key const & key) const
{
auto const keyToAgeId = m_keyToAge.find(key);
if (keyToAgeId == m_keyToAge.cend())
return false;
auto const ageToKeyIt = m_ageToKey.find(keyToAgeId->second);
if (ageToKeyIt == m_ageToKey.cend())
return false;
return key == ageToKeyIt->second;
}
private:
size_t m_age = 0;
std::map<size_t, Key> m_ageToKey;
std::map<Key, size_t> m_keyToAge;
};
size_t const m_maxCacheSize;
Loader const m_loader;
std::unordered_map<Key, Value> m_cache;
KeyAge m_keyAge;
};

4
xcode/base/base.xcodeproj/project.pbxproj
View file

@ -82,6 +82,7 @@
3D78157B1F3D89EC0068B6AC /* waiter.hpp in Headers */ = {isa = PBXBuildFile; fileRef = 3D78157A1F3D89EC0068B6AC /* waiter.hpp */; };
3DBD7B95240FB11200ED9FE8 /* checked_cast_tests.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 3DBD7B94240FB11200ED9FE8 /* checked_cast_tests.cpp */; };
564BB445206E89ED00BDD211 /* fifo_cache.hpp in Headers */ = {isa = PBXBuildFile; fileRef = 564BB444206E89ED00BDD211 /* fifo_cache.hpp */; };
56290B8A206D0887003892E0 /* lru_cache.hpp in Headers */ = {isa = PBXBuildFile; fileRef = 56290B89206D0887003892E0 /* lru_cache.hpp */; };
56B1A0741E69DE4D00395022 /* random.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 56B1A0711E69DE4D00395022 /* random.cpp */; };
56B1A0751E69DE4D00395022 /* random.hpp in Headers */ = {isa = PBXBuildFile; fileRef = 56B1A0721E69DE4D00395022 /* random.hpp */; };
56B1A0761E69DE4D00395022 /* small_set.hpp in Headers */ = {isa = PBXBuildFile; fileRef = 56B1A0731E69DE4D00395022 /* small_set.hpp */; };
@ -234,6 +235,7 @@
3DBD7B94240FB11200ED9FE8 /* checked_cast_tests.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = checked_cast_tests.cpp; sourceTree = "<group>"; };
564BB444206E89ED00BDD211 /* fifo_cache.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; path = fifo_cache.hpp; sourceTree = "<group>"; };
564BB446206E8A4D00BDD211 /* fifo_cache_test.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = fifo_cache_test.cpp; sourceTree = "<group>"; };
56290B89206D0887003892E0 /* lru_cache.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; path = lru_cache.hpp; sourceTree = "<group>"; };
56B1A0711E69DE4D00395022 /* random.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = random.cpp; sourceTree = "<group>"; };
56B1A0721E69DE4D00395022 /* random.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; path = random.hpp; sourceTree = "<group>"; };
56B1A0731E69DE4D00395022 /* small_set.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; path = small_set.hpp; sourceTree = "<group>"; };
@ -433,6 +435,7 @@
3917FA56211E009700937DF4 /* get_time.hpp */,
3917FA52211E008C00937DF4 /* clustering_map.hpp */,
564BB444206E89ED00BDD211 /* fifo_cache.hpp */,
56290B89206D0887003892E0 /* lru_cache.hpp */,
675341851A3F57E400A0A8C3 /* array_adapters.hpp */,
675341861A3F57E400A0A8C3 /* assert.hpp */,
675341871A3F57E400A0A8C3 /* base.cpp */,
@ -551,6 +554,7 @@
675341E31A3F57E400A0A8C3 /* math.hpp in Headers */,
3446C6731DDCA96300146687 /* levenshtein_dfa.hpp in Headers */,
56B1A0751E69DE4D00395022 /* random.hpp in Headers */,
56290B8A206D0887003892E0 /* lru_cache.hpp in Headers */,
675341E21A3F57E400A0A8C3 /* macros.hpp in Headers */,
672DD4C51E0425600078E13C /* observer_list.hpp in Headers */,
675341EF1A3F57E400A0A8C3 /* rolling_hash.hpp in Headers */,